Now the variable normalize gets the value False when the user specifies vmin and vmax.
vmin and vmax can be defined when using
mp.plot(...,  shading = {"normalize" = [vmin, vmax]}, ...)
If nothing is set by the user the standard value is 
"normalize" = [None, None].
If any of the two entries are None, then the variable normalize in Viewer.py gets the value True, and vmin and vmax are chosen inside utils.py in get_colors.

We don't need the variable normalize, since the condtion in get_colors can be written based on vmin and vmax